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-rw-r--r--dns.c356
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+/* $OpenBSD: dns.c,v 1.38 2018/02/23 15:58:37 markus Exp $ */
+
+/*
+ * Copyright (c) 2003 Wesley Griffin. All rights reserved.
+ * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include <netdb.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+#include <stdlib.h>
+
+#include "xmalloc.h"
+#include "sshkey.h"
+#include "ssherr.h"
+#include "dns.h"
+#include "log.h"
+#include "digest.h"
+
+static const char *errset_text[] = {
+ "success", /* 0 ERRSET_SUCCESS */
+ "out of memory", /* 1 ERRSET_NOMEMORY */
+ "general failure", /* 2 ERRSET_FAIL */
+ "invalid parameter", /* 3 ERRSET_INVAL */
+ "name does not exist", /* 4 ERRSET_NONAME */
+ "data does not exist", /* 5 ERRSET_NODATA */
+};
+
+static const char *
+dns_result_totext(unsigned int res)
+{
+ switch (res) {
+ case ERRSET_SUCCESS:
+ return errset_text[ERRSET_SUCCESS];
+ case ERRSET_NOMEMORY:
+ return errset_text[ERRSET_NOMEMORY];
+ case ERRSET_FAIL:
+ return errset_text[ERRSET_FAIL];
+ case ERRSET_INVAL:
+ return errset_text[ERRSET_INVAL];
+ case ERRSET_NONAME:
+ return errset_text[ERRSET_NONAME];
+ case ERRSET_NODATA:
+ return errset_text[ERRSET_NODATA];
+ default:
+ return "unknown error";
+ }
+}
+
+/*
+ * Read SSHFP parameters from key buffer.
+ */
+static int
+dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
+ u_char **digest, size_t *digest_len, struct sshkey *key)
+{
+ int r, success = 0;
+ int fp_alg = -1;
+
+ switch (key->type) {
+ case KEY_RSA:
+ *algorithm = SSHFP_KEY_RSA;
+ if (!*digest_type)
+ *digest_type = SSHFP_HASH_SHA1;
+ break;
+ case KEY_DSA:
+ *algorithm = SSHFP_KEY_DSA;
+ if (!*digest_type)
+ *digest_type = SSHFP_HASH_SHA1;
+ break;
+ case KEY_ECDSA:
+ *algorithm = SSHFP_KEY_ECDSA;
+ if (!*digest_type)
+ *digest_type = SSHFP_HASH_SHA256;
+ break;
+ case KEY_ED25519:
+ *algorithm = SSHFP_KEY_ED25519;
+ if (!*digest_type)
+ *digest_type = SSHFP_HASH_SHA256;
+ break;
+ case KEY_XMSS:
+ *algorithm = SSHFP_KEY_XMSS;
+ if (!*digest_type)
+ *digest_type = SSHFP_HASH_SHA256;
+ break;
+ default:
+ *algorithm = SSHFP_KEY_RESERVED; /* 0 */
+ *digest_type = SSHFP_HASH_RESERVED; /* 0 */
+ }
+
+ switch (*digest_type) {
+ case SSHFP_HASH_SHA1:
+ fp_alg = SSH_DIGEST_SHA1;
+ break;
+ case SSHFP_HASH_SHA256:
+ fp_alg = SSH_DIGEST_SHA256;
+ break;
+ default:
+ *digest_type = SSHFP_HASH_RESERVED; /* 0 */
+ }
+
+ if (*algorithm && *digest_type) {
+ if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
+ digest_len)) != 0)
+ fatal("%s: sshkey_fingerprint_raw: %s", __func__,
+ ssh_err(r));
+ success = 1;
+ } else {
+ *digest = NULL;
+ *digest_len = 0;
+ success = 0;
+ }
+
+ return success;
+}
+
+/*
+ * Read SSHFP parameters from rdata buffer.
+ */
+static int
+dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
+ u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
+{
+ int success = 0;
+
+ *algorithm = SSHFP_KEY_RESERVED;
+ *digest_type = SSHFP_HASH_RESERVED;
+
+ if (rdata_len >= 2) {
+ *algorithm = rdata[0];
+ *digest_type = rdata[1];
+ *digest_len = rdata_len - 2;
+
+ if (*digest_len > 0) {
+ *digest = xmalloc(*digest_len);
+ memcpy(*digest, rdata + 2, *digest_len);
+ } else {
+ *digest = (u_char *)xstrdup("");
+ }
+
+ success = 1;
+ }
+
+ return success;
+}
+
+/*
+ * Check if hostname is numerical.
+ * Returns -1 if hostname is numeric, 0 otherwise
+ */
+static int
+is_numeric_hostname(const char *hostname)
+{
+ struct addrinfo hints, *ai;
+
+ /*
+ * We shouldn't ever get a null host but if we do then log an error
+ * and return -1 which stops DNS key fingerprint processing.
+ */
+ if (hostname == NULL) {
+ error("is_numeric_hostname called with NULL hostname");
+ return -1;
+ }
+
+ memset(&hints, 0, sizeof(hints));
+ hints.ai_socktype = SOCK_DGRAM;
+ hints.ai_flags = AI_NUMERICHOST;
+
+ if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
+ freeaddrinfo(ai);
+ return -1;
+ }
+
+ return 0;
+}
+
+/*
+ * Verify the given hostname, address and host key using DNS.
+ * Returns 0 if lookup succeeds, -1 otherwise
+ */
+int
+verify_host_key_dns(const char *hostname, struct sockaddr *address,
+ struct sshkey *hostkey, int *flags)
+{
+ u_int counter;
+ int result;
+ struct rrsetinfo *fingerprints = NULL;
+
+ u_int8_t hostkey_algorithm;
+ u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
+ u_char *hostkey_digest;
+ size_t hostkey_digest_len;
+
+ u_int8_t dnskey_algorithm;
+ u_int8_t dnskey_digest_type;
+ u_char *dnskey_digest;
+ size_t dnskey_digest_len;
+
+ *flags = 0;
+
+ debug3("verify_host_key_dns");
+ if (hostkey == NULL)
+ fatal("No key to look up!");
+
+ if (is_numeric_hostname(hostname)) {
+ debug("skipped DNS lookup for numerical hostname");
+ return -1;
+ }
+
+ result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
+ DNS_RDATATYPE_SSHFP, 0, &fingerprints);
+ if (result) {
+ verbose("DNS lookup error: %s", dns_result_totext(result));
+ return -1;
+ }
+
+ if (fingerprints->rri_flags & RRSET_VALIDATED) {
+ *flags |= DNS_VERIFY_SECURE;
+ debug("found %d secure fingerprints in DNS",
+ fingerprints->rri_nrdatas);
+ } else {
+ debug("found %d insecure fingerprints in DNS",
+ fingerprints->rri_nrdatas);
+ }
+
+ /* Initialize default host key parameters */
+ if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
+ &hostkey_digest, &hostkey_digest_len, hostkey)) {
+ error("Error calculating host key fingerprint.");
+ freerrset(fingerprints);
+ return -1;
+ }
+
+ if (fingerprints->rri_nrdatas)
+ *flags |= DNS_VERIFY_FOUND;
+
+ for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
+ /*
+ * Extract the key from the answer. Ignore any badly
+ * formatted fingerprints.
+ */
+ if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
+ &dnskey_digest, &dnskey_digest_len,
+ fingerprints->rri_rdatas[counter].rdi_data,
+ fingerprints->rri_rdatas[counter].rdi_length)) {
+ verbose("Error parsing fingerprint from DNS.");
+ continue;
+ }
+
+ if (hostkey_digest_type != dnskey_digest_type) {
+ hostkey_digest_type = dnskey_digest_type;
+ free(hostkey_digest);
+
+ /* Initialize host key parameters */
+ if (!dns_read_key(&hostkey_algorithm,
+ &hostkey_digest_type, &hostkey_digest,
+ &hostkey_digest_len, hostkey)) {
+ error("Error calculating key fingerprint.");
+ freerrset(fingerprints);
+ return -1;
+ }
+ }
+
+ /* Check if the current key is the same as the given key */
+ if (hostkey_algorithm == dnskey_algorithm &&
+ hostkey_digest_type == dnskey_digest_type) {
+ if (hostkey_digest_len == dnskey_digest_len &&
+ timingsafe_bcmp(hostkey_digest, dnskey_digest,
+ hostkey_digest_len) == 0)
+ *flags |= DNS_VERIFY_MATCH;
+ }
+ free(dnskey_digest);
+ }
+
+ free(hostkey_digest); /* from sshkey_fingerprint_raw() */
+ freerrset(fingerprints);
+
+ if (*flags & DNS_VERIFY_FOUND)
+ if (*flags & DNS_VERIFY_MATCH)
+ debug("matching host key fingerprint found in DNS");
+ else
+ debug("mismatching host key fingerprint found in DNS");
+ else
+ debug("no host key fingerprint found in DNS");
+
+ return 0;
+}
+
+/*
+ * Export the fingerprint of a key as a DNS resource record
+ */
+int
+export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
+{
+ u_int8_t rdata_pubkey_algorithm = 0;
+ u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
+ u_int8_t dtype;
+ u_char *rdata_digest;
+ size_t i, rdata_digest_len;
+ int success = 0;
+
+ for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
+ rdata_digest_type = dtype;
+ if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
+ &rdata_digest, &rdata_digest_len, key)) {
+ if (generic) {
+ fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
+ hostname, DNS_RDATATYPE_SSHFP,
+ 2 + rdata_digest_len,
+ rdata_pubkey_algorithm, rdata_digest_type);
+ } else {
+ fprintf(f, "%s IN SSHFP %d %d ", hostname,
+ rdata_pubkey_algorithm, rdata_digest_type);
+ }
+ for (i = 0; i < rdata_digest_len; i++)
+ fprintf(f, "%02x", rdata_digest[i]);
+ fprintf(f, "\n");
+ free(rdata_digest); /* from sshkey_fingerprint_raw() */
+ success = 1;
+ }
+ }
+
+ /* No SSHFP record was generated at all */
+ if (success == 0) {
+ error("%s: unsupported algorithm and/or digest_type", __func__);
+ }
+
+ return success;
+}